Flash tube apparatus

ABSTRACT

A system is provided for producing repeatable, short-duration pulses of infrared radiation suitable for optical purposes. Radiation is produced by electrically parallel arcs, which are induced within a flash tube containing an inert gas at low pressure and are guided into paths in the form of nonplanar loops whose branches are adjacent one another. The flash tube, which is of a volume sufficient to maintain relatively low gas density during arc discharge, is shaped to accommodate the arc paths and to provide a compact optical source for the radiation.

United States Patent Giannini 1 1 Mar. 21, 1972 [54] FLASH TUBE APPARATUS 3,267,328 8/1966 Girard ..315/241x I 3,414,765 12/1968 McKnight et al. ....315/243x [721 lnvemmcab'ielM' Giannini 3,480,831 11 1969 Wuerker et a1. ..31s/243 x [73] Assignee: Giannini Institute Primary Examiner-Roy Lake [22] Filed: May 1969 Assistant ExaminerLawrence J. Dahl [5 1] Int. Cl. ..H0lj 17/04, H05b 37/00.

[58] Field of Search ..313/204, 184; 315/241 P, 241, 315/243, 52

[56] References Cited UNITED STATES PATENTS 2,102,189 12/1937 Barclay ..313/204 2,264,081 11/1941 Jost et al.. ..3l5 /52 2,843,801 7/1958 Kreft ..313/184 X 3,024,383 3/1962 Doering ..313/204 X Appl. No.: 828,526

US. Cl ..3l3/204, 315/241 POWER SUPPLY Attorney-Fraser and Bogucki [57] ABSTRACT A system is provided for producing repeatable, short-duration pulses of infrared radiation suitable for optical purposes. Radiation is produced by electrically parallel arcs, which are induced within a flash tube containing an inert gas at low pressure and are guided into paths in the form of nonplanar loops whose branches are adjacent one another. The flash tube, which is of a volume sufficient to maintain relatively low gas density during arc discharge, is shaped to accommodate the arc paths and to provide a compact optical source for the radiation.

4 Claims, 8 Drawing Figures TRIGGER CIRCUIT PAIENTEDMAR21 I972 SHEET 1 [IF 2 INVENTOR.

GABRIEL H. GIANNINI ATTOR Y5 FAIENTEDMARZI I972 3. 651 ,366

sum 2 0F 2 CAPACITOR BANK CAPACITOR v BANK INVENTOR.

GABRIEL u. GIMHHNI ATTORNE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to systems for producing rapidly repeatable, short-duration pulses of high intensity radiation, by means of induced arc discharges within a gas filled container, and particularly to flash tubes for producing flashes of infrared light for long range photography.

2. Description of the Prior Art Flash tubes of the type currently available for illumination are generally divided into two categories structurally. These are linear tubesi. e., those with a substantially straight discharge path-and tubes with a helical discharge. Rectilinear tubes are useful for broad illumination purposes but do not lend themselves to producing narrow or approximately symmetrical or well-defined light beams because of the problem of focusing created by their shapes. The problem is made even more severe by the substantial length which must be provided in such a tube for extremely high energy illumination. Helical tubes are more suited for this use because the discharge path may be directed within and around the focus of an optical system such as a mirror. However, the cylindrical region within the discharge helix is not luminous and thus the light source is necessarily defocused to this extent. Furthermore, a large amount of glass or quartz is in the way of the radiation.

Another problem resulting from attempts to use such tubes is due to the inherent inductance of the tubes. This is not too noticeable with smaller, low-powered tubes because the inductance is low. However, with the increase in size necessitated by increases in energy levels for greater illumination, the minimum inductance for a given tube configuration progressively increases, while at the same time the inductance of the capacitor bank also increases with size.

In previously known flash tubes of the type to which the invention relates, minimum limits have been placed on the brevity of flashes by the inductance of the discharge circuit paths. Reduction of inductance in the external circuitry which becomes less and less feasible as power increases still leaves a certain minimum inductance contributed by the discharge path within the tube itself which prevents reduction of the flash duration at practical energy levels to less than a few milliseconds. The use of larger tubes to handle higher energy levels heightens the problem of the discharge inductance effect on flash duration. If the discharge inductance can be reduced, higher peak power levels may be achieved for shorter durations, thus providing adequate illumination for photographic strobes, without increasing the average power dissipation.

In the past, where extremely intense light flashes were desired, the permissible diameter of the discharge has been limited by constriction of the tube structure so as to both restrict the discharge diameter and effect an increase in the instantaneous pressure of the gaseous region occupied by the discharge. This, however, tends to produce a flash of light which peaks at the upper portion of the visible frequency spectrum and beyond. Thus, while increases in light emission have been realized by this approach, the problems of energy dissipation in the tube walls are also increased, Furthermore, such stroboscopic flash tubes are not suitable as infrared light sources, their efficiency being very low in this region of the spectrum.

The intensity of radiation produced by previously available flash tubes has been limited by the losses caused by the contact of the discharge with the walls of the tube with consequent early deterioration of the tube. Energy production has also been limited by the increasing inductance of arcs with increasing size. Pulse repetition rates, which are closely related to the total energy handled by the tube have also accordingly been limited.

It is therefore a general object of the present invention to provide improved structural configurations for stroboscopic arc tubes.

It is a further object of my invention to cause the discharge to take place between parallel paths so that they may attract to one another away from the tube walls.

It is a further object of my invention to provide such tubes capable of operating at very high energy levels with controllably short light flashes.

It is a particular object of my invention to provide such tubes efiective at emitting radiation in the infrared region for night photography and reconnaissance.

SUMMARY OF THE INVENTION The purposes and objectives of the invention may be realized by a flash tube system within which electric arcs induced in a gaseous atmosphere produce rapidly repeatable, short-duration pulses of high intensity radiation suitable for photographic and other optical and viewing purposes such as laser pumps, television and other viewing systems whose energy is concentrated at a selected range of the spectrum, particularly at the near infrared, that is, in the range of 0.7-0.9 microns wavelength. 7

Particular arrangements in accordance with the invention may provide arc paths in the form of nonplanar loops with adjacent branches conducting discharge current in opposite directions. For two-branch shapes, the paths resemble Us folded upon themselves. Arcs following such paths are of relatively small inductance because the minimizing of the area enclosed by the current path in accordance with the invention permits the realization of a minimum inductance for the device. Thus the doubling back of the discharge path in such a fashion results in an effective inductance much lower than has hitherto been realized. Systems in accordance with this embodiment of the invention thus are capable of being energized by large capacitor banks of substantially large inductance without contributing substantially to the total inductance and therefore to emit radiation in relatively brief flashes since a significant limitation on are brevity, arc inductance, is thereby substantially diminished, even at greatly increased energy levels of operation.

Such flash tubes in the form of nonplanar loops with contiguously adjacent branches also provide a relatively compact radiation source for the discharges accompanying the arcs, so that emitted radiation is suitable for optical purposes, for which light from diffuse sources or sources of high aspect ratios is unsatisfactory.

In accordance with another aspect of the invention, particular arrangements thereof are fabricated to develop an increased volume for the arc discharges within the tube envelope, which is approximately equal to the volume such discharges would have in unconfined space. As a result the relatively low pressure within the flash tube is not increased substantially during the discharge. This advantageously provides radiation whose energy is concentrated more in the infrared region of the spectrum, thus improving the effectiveness of the radiation source for night-time illumination without detection.

In accordance with an aspect of the invention, one particular embodiment thereof provides for a plurality of parallel discharge paths within a single tube. Each individual discharge is driven by a separate power supply with triggering being effected in common. Operation in parallel in this fashion advantageously permits a reduction in the effective inductance of the system, which, because of the lower power of the individual systems, occurs both in the external circuitry and in the inductance presented by the arc discharges within the tube, when compared with the inductance presented by conventional tube configurations driven at comparable peak energy levels. Moreover, the parallel discharge arcs within this embodiment tend to move together because of the magnetic field forces, thus making the light even more intense and reducing the amount of heat energy which is directed to the walls of the tube itself. The useful life of the tube is thus lengthened because the structure runs cooler and is less likely to darken with use.

Flash tube apparatus in accordance with theinvention advantageously serve to reduce the self-inductance of the arc discharge materially, thus permitting the transfer. of peak energies to the discharge tube in much shorter time intervals and in controllable wave form than has heretofore been possible. It therefore becomes feasible to control the time interval of the discharge so as to develop a suitable pulse of radiation. Accordingly in another particular arrangement in accordance with the invention, there is provided a particular energy storage circuit for controlling the delivery of energy to the arc discharge at a predetermined rate, thus controlling the intensity and duration of the discharge as desired. This includes a plurality of storage capacitors in parallel circuit branches, some of which are in series with inductors of different values of inductance. Thus the delivery of energy to the are from the respective storage capacitors may be delayed by varying amounts with the desired control of discharge parameters as described, by means of the proper selection of the values of the pulse shaping network elements selected.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention may be had from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of one particular flash tube arrangement in accordance with the invention;

FIG. 2 is a perspective view of another particular flash tube arrangement in accordance with the invention;

FIG. 3 is a sectional view taken along the line 33 of FIG.

FIG. 4 is a perspective view of still another particular flash tube arrangement in accordance with the invention;

FIG. 5 is a perspective view of yet another particular flash tube arrangement in accordance with the invention;

FIG. 6 is a sectional view taken along the line 6-6 of FIG.

FIG. 7 is a schematic representation of a system including electrical circuitry associated with the above mentioned arrangements in accordance with the invention; and

FIG. 8 is a schematic representation of a second system in accordance with the invention including circuitry for controllingflash tube discharge.

FIG. 1 represents one particular arrangement in accordance with the invention in which a flash tube 10 is shown having an envelope 12 formed in a U-shape folded upon itself and with two separate electrodes 14, 16 positioned at opposite ends of the folded U-shape. Although the electrodes 14, 16 are spatially adjacent one another, the discharge path within the tube 12 runs the extend of the folded U-shaped tube from one end to the other back and forth between electrodes 14, 16. Accordingly, the discharge path volume of the tube 10 is substantially reduced, compared with a straight or U-shaped tube, thus providing a more compact and intense light source. Moreover, because the envelope 12 of the tube 10 is folded back upon itself, thus directing the discharge path of the are between the electrodes 14, 16 to establish essentially parallel paths of equal magnitude current flowing in opposite directions, the magnetic field from-one branch virtually cancels the magnetic field from the other branch so that the discharge inductance is substantially reduced, compared to that which is presented by a linear discharge path of the prior art.

FIG. 2 and the corresponding sectional view of FIG. 3 represent another embodiment of the invention in the form of a tube 20 having an envelope 22 divided lengthwise into four separate compartments by internal partitions 27 and 28 which are substantially orthogonally positioned relatively to each other. Electrodes 24 and 26 are positioned at one end of the tube spatially adjacent each other but separated physically and electrically by the partitions 27, 28. As shown, the partition 27 has openings near the end of the envelope 22 remote from the position of the two electrodes 24, 26, which openings in each instance permit the arc discharge to pass from one side of the partition 27 to the other. Partition 28, on the other hand, has an opening adjacent the end of the envelope 22 in which the electrodes 24, 26 are mounted. However, the opening in the partition 28 is on the opposite side of the partition 27 from the electrodes 24, 26. Accordingly, in the tube 20, the discharge path extends the length of the envelope 22 four times, extending from the electrode 24 to the remote end of the envelope 22, through the opening in the partition 27, back to the electrode end of the envelope 22, through the opening in the partition 28, back to the end of the-envelope 22 remote from the electrodes, through the second opening in the partition 27, and finally to the electrode end of envelope 22 to the electrode 26. The discharge path in the tube 20 is somewhat similar to the path traversed by the discharge in the tube 10 of FIG. I; however, in addition the envelope 22 has an enlarged diameter by comparison with the envelope l2 and the discharge within the tube 20 is less confined and thus less subject to a transient increase in pressure during firing than is the tube 10 of FIG. 1. This configuration advantageously avoids constriction of the arc discharge in its traversal between the electrodes 24, 26, allowing the discharge to occupy substantially the volume it would occupy in unconfined space with the result that a larger portion of the radiation emitted falls in the infrared range than if the discharge were confined. Moreover, the tube 20 of FIGS. 2 and 3 is designed to contain a gas at reduced pressure. This particular configuration eliminates the transient increase in pressure during discharge which is commonly encountered in tubes having more confining envelopes, thus providing a compact light source presenting a reduced discharge inductance and developing radiation in the useful infrared range. Accordingly, the configuration of the tube 20 of FIGS. 2 and 3 is preferred for radiation rich in the infrared spectrum.

FIG. 4 represents still another embodiment of the present invention in which a tube 40 comprises an envelope 42 having a plurality of pairs of electrodes 44A, 44B, 44C and 46A, 46B, 46C positioned at opposite ends thereof. The benefits from the use of configurations of the type depicted in FIG. 4 are a substantial reduction in the inherent inductance both within and without the tube by virtue of the fact that a plurality of smaller discharges are established in parallel from parallel external circuits, as well as the fact that the tube is of increased diameter relative to its length without constriction of the arc discharge so that again the arc discharges occur at reduced pressure to provide radiation rich within the infrared range. Moreover, with this particular configuration as depicted in FIG. 4, the separate discharges which occur between respective pairs of opposed electrodes, such as 44A and 46A, occurring concurrently in parallel are directed toward one another by the accompanying magnetic fields in accordance with the well known pinch effect and away from the walls of envelope 42. Consequently, the thermal shock from heat dissipation in the walls of the envelope 42 is reduced, as is also the effect on the envelope 42 with use. Both of these beneficial results serve to increase the useful life of the arc discharge tube 40.

FIG. 5 represents still another particular arrangement in accordance with the invention in which a tube 50 is shown comprising a single envelope 52 divided by a partition 57 running substantially its entire length except for the space at one end of the envelope 52. At the opposite end of envelope 52 there are positioned two pairs of electrodes 54A, 54B and 56A, 56B disposed on opposite sides of the partition 57. The envelope 52 is of relatively increased diameter without constriction for restricting the discharges between the respective pairs of electrodes and contains a suitable gas, such as krypton, at reduced pressure. Consequently, the two discharges occurring within the envelope 52 between opposed pairs of electrodes, such as 54A and 56A, are directed along the extent of the envelope 52 around the end of the partition 57 and return. As a consequence, the magnetic fields of the respective current branches tend to cancel each other in the manner already described in connection with FIG. 1, for example, so that the discharge inductance is effectively reduced. The use of parallel pairs of electrodes and a corresponding plurality of separate discharges also permits reduction of the discharge inductance as well as of the minimum inductance which may be designed into the associated electrical circuitry. Moreover, as already described in connection with FIG. 4, the parallel discharge arcs are directed toward one another by the associated magnetic fields and away from the walls of the envelope 52, thus insuring longer operative life for the tube 50.

FIG. 7 represents an operative system in schematic form, including a particular tube 80 similar to that which is shown in FIG. 4. In FIG. 6, the tube 70 is shown in sectional form as comprising in envelope 72 within which are contained opposed pairs of electrodes 74A, 74B and 76A, 76B between which parallel discharges take place. Also shown is an igniter electrode 75 which is used to initiate an arc discharge within the envelope 72. As soon as such a discharge is initiated by the igniter electrode 75 operating in cooperation with one or more of the other electrodes 74 and 76 within the envelope 72, the arc discharge transfers to the major discharge paths between the opposed electrodes 74 and 76.

In the circuitry of FIG. 7, the system is shown being driven from a single power supply 81 connected to provide current to separate energy storage capacitor banks 82 and 83 in distinct branches of the circuit. Each capacitor bank such as 82 is the source for the energy of the discharge across a particular pair of electrodes within the envelope 72, such as electrodes 74B and 76B. Resistors 84 and 85 are inserted in series legs between the power supply 81 and the respective capacitor banks 82 and 83. An ignition circuit is connected to provide suitable energy in the form of a high voltage pulse supplied to the igniter electrode 75. This circuit is connected to a tap in a bleeder network comprising resistors 86 connected across the opposite terminals of the power supply 81. A transformer 87 has its primary winding connected in series with an ignition switch 88 for developing an ignition pulse which may be applied from the secondary winding of the transformer 87 to the igniter electrode 75.

In the operation of this circuit, the capacitor banks 82 and 83 are permitted to charge to power supply voltage which may be on the order of several hundred up to a few thousand volts DC. Each capacitor bank such as 82 preferably stores a few thousands of watts-seconds of energy. When the tube 72 is to be fired, the ignition switch 88 is closed and the resulting high voltage applied to the igniter electrode 75 initiates the discharge within the tube 72 which quickly transfers to the main electrodes as already described.

In each of the arrangements of flash tubes depicted in FIGS. 1 through 6 of the drawings, the igniting mechanism has been omitted for purposes of simplicity. It will be understood that each of the tube configurations of FIGS. 1 through 6 may include an igniter electrode similar to the electrode 75 shown in the tube of FIG. 7. Alternatively, as known in the art, the ignition of the flash tubes shown and described herein may be realized by the use of a thin wire electrode, preferably encircling the tube. Application of a pulse to such a coil serves to initiate ionization of the gas within the tube so that the desired discharge between the tube electrodes is established and maintained under the voltage applied from associated capacitor banks. In those arrangements providing a single pair of electrodes in a flash tube, only a single capacitor bank is required. In the general case, as many separate capacitor banks isolated from one another are provided as there are pairs of electrodes and discharge paths in a given tube.

Such an arrangement is shown schematically in FIG. 8 in which a single flash tube 90, for example one similar to the tube depicted in greater detail in FIG. 3B, is shown having a single pair of electrodes 94, 96 mounted on opposite sides of a partition 97 to develop a concentrated U-shaped discharge. The circuit of FIG. 8 shows a capacitor bank 102 connected to supply electrical energy to the electrodes 94, 96 when the tube 90 is fired. The capacitor bank 102 is charged from a power supply 101 by series resistors 99. The power supply of 101 also provides power to a trigger circuit 108 which is connected to a coil 100 surrounding the tube 90. Ignition of discharge within the tube is initiated by ionization energy from the coil when the trigger circuit 108 is activated.

The capacitor bank 102 is shown comprising three branch capacitors 103, 104 and which are arranged with inductances 106 and 107 to control the period of the arc discharge within the tube 90 in accordance with an aspect of the invention. By virtue of the various arrangements of the invention described hereinabove which have served to reduce the inductance of the flash tube apparatus and associated circuitry, it may become desirable under certain circumstances to provide arrangements for continuing the flash tube discharge for a predetermined interval. The circuitry shown within the capacitor bank 102 in FIG. 8 serves to accomplish this objective. Upon initiation by activation of the triggered circuit 108, the discharge within the tube 90 is supplied energy initially from the capacitor 103 which is connected across the electrodes 94, 96 without any series inductance. The series inductance 106 serves to delay the delivery of energy from the capacitor 104 for a short period of time, so that the capacitor 104 can take over as the energy stored in capacitor 103 becomes depleted. The inductance 107 in series with the capacitor 105 is somewhat larger than the inductance 106, thus serving to provide a further delay of the transfer of energy from the capacitor 105 to the arc discharge of the tube 90. In practice, particular values of 5 microhenries and 10 microhenries of inductance have been found satisfactory for the inductances 106 and 107, respectively. An arrangement of this type controls the arc discharge with somewhat increased intensity but with the duration extended from two to three times over that which is obtained from the discharge of a single capacitor arrangement without any time delay introduced by the series inductances.

In the above described systems in accordance with the invention in which radiant energy in the infrared range is desired, krypton gas is suitable as the inert gas contained within the tube envelope. However, many other gases may be employed in tube configurations in accordance with the invention depending on the spectrum desired. In those arrangements in accordance with the invention in which a plurality of discharge paths are provided, it will be understood that the discharge paths are not limited to the number shown, but may be a greater or lesser number, if desired.

Although there have been described hereinabove specific arrangements of flash tube apparatus in accordance with the invention for the purpose of illustrating the manner in which ,the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention.

What is claimed is:

1. Flash tube apparatus constructed for the simultaneous production of a plurality of discrete, substantially parallel, stroboscopic arc discharges in the same direction to provide electromagnetic radiation in the infrared region comprising:

an envelope of material transparent to infrared radiation;

an inert gas contained within said envelope;

a plurality of non-coplanar pairs of electrodes extending into said envelope disposed to establish arc discharges equal in number to the number of pairs of electrodes, each of said pairs of electrodes being adapted for connection to a separate electrical energy supply means; and

partitioning means within said envelope and forming with the walls of said envelope a plurality of individual passages, each of said passages being elongated and communicating with an adjacent passage at one end thereof to establish a series path for said are discharges, the lateral dimensions of each of said passages corresponding approximately to the lateral dimensions of an arc discharge in unconfined space and wherein said passages are said inert gas is krypton at substantially atmospheric pressure.

independent,

Flash tube apparatus constructed to control a plurality of pulsed, substantially parallel electric arc discharges within a confined region, to provide a compact optical source of radiation, comprising:

an enclosing envelope of a transparent material of volume sufficient to maintain a relatively low gas density during arc discharge;

a gas confined within said envelope; and at least two pairs of electrodes extending through said envelope into a confined gas region, said electrode pairs being disposed in non-coplanar relation and to provide independent, substantially parallel discharge are paths of reduced inductance, said pairs of electrodes being adapted for connection to separate sources of electrical energy for providing discrete electrical pulses simultaneously to all of said pairs of electrodes in the same direction to cause attraction of said arcs toward one another and away from the tube walls;

said envelope is shaped and said pairs of electrodes are positioned to direct said discharges to follow at least four adjacent, substantially parallel paths in at least two of which the discharge current flows in opposite directions.

4. Flash tube apparatus constructed to control a plurality of independent, pulsed, substantially parallel electric are discharges within a confined region, comprising: an enclosing envelope of transparent material;

a gas confined within said envelope; a partition dividing said envelope into two parallel regions;

and

at least two pairs of electrodes extending through said envelope into a confined gas region, said electrode pairs being disposed to provide independent, substantially parallel, non-coplanar discharge are paths of reduced inductance, each pair of electrodes comprising a first electrode on one side of said partition and a second electrode on the other side of said partition, said partition further being shaped to bring said regions into communication in an area distal said electrodes, said electrodes being adapted, for connection to means for establishing discrete, independent, substantially parallel discharges between the electrodes of each electrode pair moving from said first electrodes to said second electrodes to cause attraction of said arcs toward one another and away from the tube walls. 

1. Flash tube apparatus constructed for the simultaneous production of a plurality of discrete, substantially parallel, stroboscopic arc discharges in the same direction to provide electromagnetic radiation in the infrared region comprising: an envelope of material transparent to infrared radiation; an inert gas contained within said envelope; a plurality of non-coplanar pairs of electrodes extending into said envelope disposed to establish arc discharges equal in number to the number of pairs of electrodes, each of said pairs of electrodes being adapted for connection to a separate electrical energy supply means; and partitioning means within said envelope and forming with the walls of said envelope a plurality of individual passages, each of said passages being elongated and communicating with an adjacent passage at one end thereof to establish a series path for said arc discharges, the lateral dimensions of each of said passages corresponding approximately to the lateral dimensions of an arc discharge in unconfined space and wherein said passages are disposed substantially parallel to one another so that the arc discharge is directed back and forth in substantially parallel paths, whereby the area enclosed by the overall arc discharge path is minimized.
 2. Flash tube apparatus in accordance with claim 1 wherein said inert gas is krypton at substantially atmospheric pressure.
 3. Flash tube apparatus constructed to control a plurality of independent, pulsed, substantially parallel electric arc discharges within a confined region, to provide a compact optical source of radiation, comprising: an enclosing envelope of a transparent material of volume sufficient to maintain a relatively low gas density during arc discharge; a gas confined within said envelope; and at least two pairs of electrodes extending through said envelope into a confined gas region, said electrode pairs being disposed in non-coplanar relation and to provide independent, substantially parallel discharge arc paths of reduced inductance, said pairs of electrodes being adapted for connection to separate sources of electrical energy for providing discrete electrical pulses simultaneously to all of said pairs of electrodes in the same direction to cause attraction of said arcs toward one another and away from the tube walls; said envelope is shaped and said pairs of electrodes are positioned to direct said discharges to follow at least four adjacent, substantially parallel paths in at least two of which the discharge current flows in opposite directions.
 4. Flash tube apparatus constructed to control a plurality of independent, pulsed, substantially parallel electric arc discharges within a confined region, comprising: an encloSing envelope of transparent material; a gas confined within said envelope; a partition dividing said envelope into two parallel regions; and at least two pairs of electrodes extending through said envelope into a confined gas region, said electrode pairs being disposed to provide independent, substantially parallel, non-coplanar discharge arc paths of reduced inductance, each pair of electrodes comprising a first electrode on one side of said partition and a second electrode on the other side of said partition, said partition further being shaped to bring said regions into communication in an area distal said electrodes, said electrodes being adapted, for connection to means for establishing discrete, independent, substantially parallel discharges between the electrodes of each electrode pair moving from said first electrodes to said second electrodes to cause attraction of said arcs toward one another and away from the tube walls. 